Green energy firms have long been popular ventures for entrepreneurs, but nuclear power has largely been ignored, thanks to the extreme cost, safety issues and the worries about nuclear proliferation that are usually associated with such an undertaking.

But a small group of nuclear scientists believe they can change things. By building new types of reactors, some of which reuse spent fuel rods from massive â€“ and often ageing â€“ power plants, they aim to commercialise cheaper, safer replacements to transform the industry....